Automotive emissions control is a mature industry. Automakers and suppliers have been challenged to control and reduce vehicle tailpipe emissions by the U.S. Clean Air Act in 1965 and subsequent legislation in other countries. Although base engine emissions of controlled exhaust products have been reduced significantly over the past thirty years, compliance with periodically decreasing tailpipe limits has been made possible through the use of catalytic converters.
A catalytic converter helps complete the combustion of hydrocarbon (HC) and carbon monoxide (CO) emissions and may also reduce NO.sub.x emissions. It was discovered early in their development that the lead additive in leaded gasoline acted to poison the catalyst, making its effective life only a few thousand miles. For this reason, countries with strict emission regulations also require the use of unleaded gasoline in automotive vehicles to prevent damage to their catalytic converters. However, some countries have begun regulating vehicle emissions before an adequate infrastructure is in place to provide unleaded fuel. Vehicles used in these countries would significantly benefit from use of an exhaust aftertreatment system that is resistant to lead poisoning.
Another obstacle to the durability of low emission catalyst systems is degradation in performance due to engine oil poison deposition. Trace amounts of zinc, phosphorus and other elements are put in engine oil as anti-wear additives. Their purpose is to protect engine parts from excessive wear during start-up, when engine oil is not coating the metal components of the engine. However, as the engine burns oil, zinc and phosphorus are exhausted through the catalytic converter, which may accelerate degradation of the catalyst's activity. Although the antiwear additives could be removed from the oil, long term durability of the engine could suffer. Low emission vehicles could benefit from exhaust aftertreatment systems with a tolerance for engine oil poisons.